This invention relates to an apparatus for measuring the deformation of a material under the influence of heat, and to a method of use of the apparatus for determining the wetting power of materials which deform under the influence of heat. More particularly, the invention has special application for measuring the deformation of pitches under the influence of heat and for determining the wetting power thereof.
These are prior art methods known for measuring the temperature at which a material, when heated, passes from the solid state to the viscous state and then to the liquid state. By these methods, the ball and ring softening point or the Durran melting point, or the Kraemer-Sarnow (KS) softening point can be determined for thermoplastic materials. However, the prior art methods do not provide information on the behavior of the materials throughout the entire interval during which they are heated.
It is often useful and necessary to know the nature of the change in the shape of a material being heated, and particularly, the changes occuring in the material in relation to a porous support, with which it is combined, and which support is not very sensitive to the action of heat, i.e., does not undergo significant structural changes. In the particular field of use of pitch binders for electrodes, it is useful to know the wetting power of the pitch because it provides an estimate of the utility of the pitch in the manufacture of electrodes. It should be noted at this point that by the term "pitches" is meant black or dark-brown solid cementitious materials which gradually liquify when heated and which are generally obtained as residua in the partial evaporation or fractional distillation of tar. Furthermore, by the term "wetting power" is meant the ability of the material, e.g., pitches, to wet or penetrate into the pores of the support upon which it is being liquified. More specifically, it is the ability of the material to be respectively adsorbed and absorbed on a porous support. In particular, it is useful to know the temperature, at which a pitch is completely absorbed in a coke support. In addition, it is useful to know how this absorption occurs, i.e., how the molten pitch penetrates the pores of the coke support. It is also appropriate to point out that by the term " coke" is generally meant a bituminous coal material from which the volatile constituents have been driven off by heat. The type of "coke" formed varies depending on temperature, position or the particles of coal from which it is formed, and although commonly artificially made can occur naturally and will generally be porous.